The present invention relates to a dampening suppression apparatus for a printing press such as an offset press, which suppresses dampening water transferred to an inking arrangement.
In an offset press, ink and water are supplied to a plate mounted on the circumferential surface of a plate cylinder. At this time, dampening water supplied to the plate surface is transferred to a form roller, and then, to an upstream ink roller, i.e., so-called dampening occurs. The dampening water transferred to the ink roller forms a thin film on the ink on the ink roller. A small amount of dampening water transferred to the ink roller makes the ink concentration uneven to degrade the printing quality. In addition, the dampening water and the ink are emulsified to cause tinting or scumming. Especially, for printed matter having a large nonimage area, the dampening water is supplied to the nonimage area of the plate surface to which the ink is not supplied. For this reason, the dampening water is easily transferred to the ink roller, and the amount of the transferred water is increased so that the above problem becomes more serious.
Conventionally, air is sprayed to the surface of the ink roller to evaporate the film-like dampening water, thereby suppressing dampening. More specifically, a gas pipe is arranged near the ink roller to extend along its axis. Air holes are axially formed in the gas pipe, and shutters corresponding to the respective air holes are provided. The shutters to be opened/closed are selected in correspondence with the nonimage area of the plate surface, and the air is supplied from the air holes to the ink roller.
In the above conventional arrangement, the air supply position can be selected by opening/closing the shutters. However, the air volume cannot be adjusted in correspondence with the amount of transferred dampening water and its position on the ink roller, because the air volume from each air hole is constant. In addition, because of the structure using the gas pipe, air supply efficiency is degraded due to the piping resistance, and the structure does not cope with a compact printing press.